Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 171858

Area Forecast Discussion
National Weather Service Marquette MI
258 PM EDT Tue Apr 17 2018

.SHORT TERM...(Today and tonight)
Issued at 504 AM EDT TUE APR 17 2018

Water vapor imagery and RAP analysis show a broad, deep mid-level
low extending from the Great Lakes to the Mid-Atlantic States. Small
embedded mid-level low developed over eastern Lake Superior last
evening, supporting the increase in lake enhanced snow that
occurred. That low is now moving se across eastern Upper MI at a
quickening pace. Ongoing lake enhanced snow under 850mb temps of -10
to -13C began to diminish slightly several hrs ago, but recently it
has picked up again as another shortwave is swinging across
central/eastern Lake Superior in the circulation around the mid-
level low. Radar trends show this increase in snow nicely as
reflectivities have increased and expanded in areal coverage. Snow
has been the much fluffier lake effect variety with snow-to-water
ratios up around 25 to 1 here at the office during the night.

Expect a few more hrs of mdt to ocnl hvy shsn from the Keweenaw into
n cntrl Upper MI, n central in particular, until aforementioned
shortwave over Lake Superior passes. With a few more hrs of snowfall
upwards of 1 in/hr at times, extended ongoing advy to 8 AM.
Thereafter, expect a rapid decrease in snow intensity as forcing
departs and 850mb temps begin to rise. Ocnl lighter snow across the
rest of west and central Upper MI will also diminish. With the
departure of deeper moisture this aftn, any lingering -shsn should
become confined to the higher terrain and may actually end
altogether. Expect high temps in the low/mid 30s.

Tonight, majority of models show some light pcpn over the higher
terrain near Lake Superior as northerly low-level winds gradually
veer ne and increase as sfc high pres ridging noses s over northern
Ontario. Skeptical that any pcpn would occur since obs don`t show
much in the way of IFR or lower cigs n of Lake Superior early this
morning. However, given the signal in most model guidance, opted to
include a mention of pcpn over the high terrain n central and far w
where upsloping would be maximized. Any pcpn that occurs would
transition from -shsn/flurries to -fzdz as temps in the low-level
moist layer rise above -10C. Low temps tonight will be in the 20s.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 255 PM EDT TUE APR 17 2018

After a very active period, we return to quiet weather with average
to above average temperatures and little to no precipitation. The
main concern (believe it or not) is actually on above-average
temperatures and the potential for increased snowmelt across the
region next week. For more discussion on the potential for snow
melt, see the hydrology discussion at the end of this product.

A general warming trend is expected into the weekend with highs in
the 40s on Thursday and Friday to lower 50s by Saturday. On
Sunday, low to mid-level winds will veer southwesterly to
westerly, respectively, in accordance with an upper-level low
passing through northern Ontario. As 850 mb temperatures warm to
5 C or greater on Sunday and Monday, surface temperatures very
well may "spring" to the upper 50s to lower 60s across at least
southern portions of the forecast area. Of course it is hard to
put much stock into forecast warm temperatures with so much snow
on the ground (especially upstream of our area in Wisconsin).
However, a healthy snowpack doesn`t always equate to colder
temperatures across Upper Michigan owing to our abundance of jack-
knife coniferous trees. Overall, Sunday and Monday look quite
warm for our area.

A cold front will sweep through the Great Lakes in the
Tuesday/Wednesday time frame with a light rain, perhaps mixing
with snow. A peek into the longer range depicts warm temperatures
persisting across the area toward the end of next week. Such a
scenario would jive with the 8-14 day temperature outlook produced
by the Climate Prediction Center.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 148 PM EDT TUE APR 17 2018

MVFR ceilings have lingered through the morning and will continue
to do so through the rest of the afternoon and into the evening
hours at all terminals, except KIWD/KCMX should see a brief break
this evening as they`re right along the leading edge of the drier
air. Light wintry precipitation continues to impact KCMX/KIWD, but
sharply reduced visibilities haven`t been reported. Tonight
through mid-day on Wednesday north to northeast flow will provide
additional lift and support for lowering ceilings through the
latter half of this TAF period. Models are fairly consistent with
ceilings dropping down into the IFR category, especially at KSAW.
However, confidence was not high enough that cloud depths will be
deep enough to support the development of freezing drizzle after
these lower ceilings fill in, so opted to only include mentions of
vicinity showers for now to hint towards the potential for some
light precipitation.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 504 AM EDT TUE APR 17 2018

Under a tight pressure gradient between high pres to the n and w and
low pres over southern Ontario, northerly winds of 20-30kt will
continue this morning across Lake Superior along with some patchy
freezing spray. Not out of the question that there could be a few
gale force gusts to 35kt over the central part of the lake. Winds
will diminish dramatically over the far w part of Lake Superior this
aftn while winds of 20-30kt continue over the e. As high pres
remains to the n and w and low pres tracks from KS this evening to
New England Thu morning, expect n to ne winds mostly in the 20-30kt
range across Lake Superior tonight thru Wed night. Winds will then
diminish to under 15kt w to e Thu/Thu night as high pres settles
over the Upper Lakes. With high pres holding over the area Fri/Sat,
winds will remain under 15kt.

Issued at 255 PM EDT TUE APR 17 2018

As confidence increases in above average temperatures next week,
so does the concern for increased snowmelt across at least the
west and southern portions of Upper Michigan. After some
discussion within the office, we`ve discovered that mid-April 2013
was eerily similar in snow depth and snow water equivalent (SWE)
to where we are now. In fact, there is *more* snow/SWE on the
ground now than in 2013, especially across the south and east. As
many may remember, the end of April 2013 was marked by much above
average temperatures (mid to upper 60s) dropping the snowpack from
30+ inches to below 5 in just a few days. Such a drop led to
considerable river flooding across southern Upper Michigan. With
above average high (and potentially low) temperatures with little
to no precipitation expected across the upper Great Lakes over the
next 7-10 days, residents across the west and south are
encouraged to stay up to date on the forecast, especially in
regions that are prone to river flooding.


Upper Michigan...
Lake Superior...
Lake Michigan...


SHORT TERM...Rolfson
LONG TERM...Borchardt
HYDROLOGY...Borchardt is the U.S. government's official web portal to all federal, state and local government web resources and services.